A design procedure based on the principles of geometrical optics, for any arbitrary amplitude and phase distributions, is described for antennas employing dielectric-cone feeds. The procedure can be used for dual-reflector antennas, reflector antennas with a subreflector supported with dielguides and reflector antennas using dielectric-cone feeds with a shaped reflecting surface of the cone materi...
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High-n.a. fibres are required for optical-fibre data links. A germania-silica-core/silica-clad fibre has been produced by an alteration to the m.c.v.d. process, by the use of helium as a lining agent and the addition of P2 O5 to the core, with a measured n.a. of 0.38 and an attenuation of less than 5 dB/km at 0.89 Â¿m wavelength.
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A novel technique for fabricating small-diameter mesa-shaped structures on semiconducting substrates is described. The mesas, which are formed by etching and selective illumination of the substrate, show very little undercutting. The technique is suited for fabricating InP and GaAs transferred-electron oscillators, as well as impatt-diode structures for millimetre-wave sources.
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Energy-balance components are evaluated for an emitting site on a copper cathode with lOOnm-thick oxide film, and show Joule heating to be more important than positive-ion bombardment, which confirms a filamentary switching model.
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A class of self-orthogonal block codes is described, which are easy to decode and to augments. They are constructed by forming parity-check equations across certain patterns of information digits arranged in a 2-dimensional array. The codes are of a rate close to the optimum for self-othogonal codes.
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The normalised frequency for single-mode cut-off in an optical fibre has been calculated as a function of the dip in the refractive index at the centre of the core. For a particular class of profiles, dip width up to 40% have a negligible effect on the propagation characteristics.
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The letter presents some reflection-amplifier results for Si double-drift pulsed and c.w. IMPATTs. Peak r.f. powers of up to 11.6 and 16.5 W with instantaneous (Â¿1 dB) bandwidths ~20% at gains >6 dB have been obtained at 10 GHz with 1- and 2-diode combinations when bias modulated with a pulsewidth of 4 Â¿s and p.r.f. of 1 kHz. A 2-diode c.w. combination has given a power of 7 W (c.w.) at 10.7 ...
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A sun-tracking beam-switching radiometer has been used at a frequency of 37 GHz to measure attenuation caused by rain on earth-space paths. The attenuation derived indirectly from data on the thermal noise emitted by the rain underestimates the true attenuation by 10 to 15% and 30 to 35% for vertical and horizontal polarisations, respectively, for elevation angles in the range 10Â°Â¿35Â°.
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High-power high-efficiency oscillator operation of hi-lo-doped GaAs impatt diodes has been obtained over a frequency range extending from 7.5 to 12 GHz. Arrays of diodes have been used to obtain up to 7.7 W at 22% efficiency. From the measured variation of output power with load resistance, it is concluded that these diodes are operating in the premature collection mode.
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A simple electronically tuned c.w. GaAs impatt/varactordiode oscillator/amplifier circuit is described which can be tuned over a 10% bandwidth at mid-X-band frequencies at a power level greater than 0.5 W as an oscillator, and greater than 0.8 W at the 6 dB-gain level as a reflection amplifier. Unambiguous electronic tuning without power jumps, frequency hops or `out-of-bandÂ¿ oscillations has bee...
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Scintillation measurements made on 2 mm microwave links at 36 and 110 GHz along a common 4.1 km path across central London are described. Results are presented which show very good agreement with the theoretical predictions of Tatarski.
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The frequency-dependent transmission properties of in-homogeneous microstrip lines are calculated by means of a waveguide model and the generalised telegraphist's equations. Examples of theoretical and experimental results are presented.
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A theoretical formula amenable to numerical computation of this effect is derived in a simple and generalised fashion from an extension of an approximate method which was developed by Feinberg for the ground-to-ground propagation over an inhomogeneous flat earth.
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A criterion for the absence of limit cycles in nonlinear multivariable systems is proposed. It is very flexible and can give less conservative results. Comparison is made with existing criteria, and it is also shown that the criterion has great attractions when reduced models are used.
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Field-effect transistors with channel doping profiles fabricated by the implantation of silicon ions into high-resistivity vapour phase epitaxial GaAs have given noise figures of 2.9 dB with an associated gain of approximately 5 dB at 10 GHz. Similar measurements on F.E.T.S fabricated in an identical manner, except for the channel fabrication, where silicon ions were implanted directly into a Cr-d...
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Low-loss single-mode fibres with GeO2-doped SiO2 cores have been made by the c.v.d. method and the loss spectrum from 0.6 to 1.8 Â¿m measured. The minimum loss of the fibre with suitably designed parameters, characterised by the refractive-index difference and the core diameter, was 0.75 dB/km at 1.05 Â¿m.
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A technique for investigating the rÃ¿le of dynamic or effective leakage current in the r.f. performance of an impatt diode is described. The technique involves the design of a device structure and microwave cavity which permits the leakage current to be varied externally by photogeneration of carriers, and is compatible with c.w. operation. Typical results for flat-profile single-drift X-band sili...
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Fifteen different electron traps have been characterised in v.p.e., l.p.e., m.b.e. and bulk-grown GaAs from d.l.t.s. experiments. An accurate description of each level is given, and allows a fruitful comparison with fragmentary previous data. A catalogue of these electron traps is provided as a working tool.
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A 3-stage hybrid m.i.c. gallium-arsenide IMPATT-diode amplifier is described with an output of 1.05 W at 9.2 GHz, a large-signal gain of 21 dB and a bandwidth to Â¿3 dB greater than 1 GHz; the amplifier is stable at all input levels. The concept of an effective radius, first proposed to explain the properties of disc capacitors, has been used successfully in the circulator design. Close attention ...
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The precise rÃ¿le of the exclusive-OR function within a thresholdlogic function is illustrated by means of a new cellular array. It is shown how this cellular array may be used to form nonlinearly separable functions. A comparison with a previously described cellular array is made.
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A new 3-terminal switching device, based on the avalanche-injection effect, is proposed. Its working principle is confirmed both by theoretical and experimental results. Experimental switching times of the order of a nanosecond have been observed.
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A method of steering nulls in linear arrays by using amplitude control, rather than phase shifters, is described. The system is extended to steer all of the independent nulls in an array of any size. The problem of grating nulls is briefly discussed, and it is shown how an automatic null-steering array can be designed.
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The dispersion and filtering characteristics of a C-section periodic structure are analysed. It is shown, that, by taking into account the influence of the inhomogeneity modes, some interesting properties of this structure appear, which can be employed in the area of microwave filtering.
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A technique is described that enables an analogue multiplier operating in the `square-rootÂ¿ mode to halve the frequency of a sinusoidal input voltage. Practical results are presented and discussed for a divide-by-4 cascade.
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